Bathing appliances such as hot tubs, swimming pools and hydromassage bath fixtures often employ a water pumping means, generally comprising an induction (asynchronous) motor and direct-coupled centrifugal water pumping means. The pump operates at a single nominal speed which is directly related to the frequency of the A.C. mains supply voltage applied to the induction motor windings as well as the number of poles used in the motor design. Motor speed directly affects the pressure and flow characteristics of the pump; one speed thereby implying only one hydraulic setpoint for the given pumping system.
Bathing appliance manufacturers may wish to install pumps with high pressure and flow capacities to ensure satisfactory operation of the appliance during peak operating conditions, for example when several people are using a hot tub at one time. However, high hydraulic output may be a hindrance with a lower bather load or if gentle circulation of the water is required.
One prior art means of reducing the flow of circulation water involves manually operating restriction valves located at the water outlets of the bathing appliance. Restricting the flow of water in one area of the appliance increases the flow to an unoccupied area, providing a crude means of regulating bath water circulation.
Another known system incorporates the use of a controller and motor-operated water restriction valve, which is designed to be coupled to the pressure output port of the water circulation pump. Activation of the controller causes the operation of the motor-operated valve, thereby selectively increasing or decreasing the flow of water to the bathing appliance.
Although various forms of water restriction valves can be installed for reasonable cost, their limited scope of operation and inability to reduce motor/pump noise and operating costs is not seen as a suitable system for many bathing appliance manufacturers.
Yet another known system incorporates a water circulation pump having a universal or “brush-operated” electric motor coupled to a variable-voltage switching device means, allowing the motor to operate at a plurality of operating speeds.
Although the use of universal motors and variable-voltage switching means will directly control motor speed and pump hydraulic performance during low-speed operation, the are a number of limitations with this technology. Universal motors operate at very-high rotational speeds in order to develop sufficient torque to equal that of an equivalent induction motor. High-rotational speeds generate significant amounts of commutatator noise and reduce motor life due to brush wear. Increasing motor power level beyond a nominal level is also problematic for this technology.
A further prior art system employs the use of two or more pumps of various hydraulic performances. Hot tubs and swimming pools are filled with water and operated over periods of many months or years, requiring the use of water sanitation means and filtering. To lower the cost of operating units that include filtering systems, a secondary circulation pump that has a smaller hydraulic performance rating than the main water pump may be incorporated. Small circulator pumps allow the continuous “turn-over” of water through the filtration means, without incurring excessive operating costs related to the operation of the larger main pump.
Although having a range of pump sizes incorporated into the bathing appliance may allow optimisation of their use and reduce the operating costs of filtering the bathing water, this arrangement is costly to manufacture, nor does it improve the “bathing sensation” to the end user.
A further prior art system employs a device known as a Variable Frequency Drive (hereinafter referred to as “VFD”) which converts the applied AC mains voltage to a variable voltage and frequency to adjust the rotational speed of the referred to induction motor and hence the speed of the connected water pump.
Bathing appliances that incorporate a VFD provide an improved bather experience by offering a nearly infinite range of hydraulic pump performance, reduced pump noise at low operating speeds and lower operating costs for water filtration and circulation that other prior art systems. Unfortunately, commercially available VFD systems have had a negligible impact on the market, despite their feature advantages, due to very high capital costs. Further, commercially available VFD systems are not designed to be operated within the confines of a bath system apparatus due to specialized electrical regulatory requirements. This restriction prevents the bather from being able to operate the VFD (adjust the water circulation rate) from the comfort of the bath due to the risk of electric shock hazard, unless an electrical isolation means is incorporated into the design, increasing costs further.
Accordingly, it is an object of the present invention to provide an improved means of varying the water pressure and flow in a bathing appliance such as hot tubs, swimming pools and hydromassage bath fixtures.